System and method for rebalancing a battery during vehicle operation

ABSTRACT

A system and method for rebalancing a battery in a vehicle during vehicle operation, the battery including a plurality of modules, is provided. The method may include determining when an automatic rebalance mode start condition is satisfied, modifying a target state of charge for the battery at least in part in response to the start condition being satisfied such that the target state of charge is raised from a standard operating value to a rebalance value, operating the vehicle with the target state of charge at the rebalance value, determining when an automatic rebalance mode end condition or an interrupt condition is satisfied, and modifying the target state of charge in response to the automatic rebalance mode end condition or the interrupt condition being satisfied such that the target state of charge is lowered from the rebalance value to the standard operating value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system and method for rebalancing a batteryduring vehicle operation.

2. Background Art

Conventional electric (EV), hybrid electric (HEV), and fuel cell (FC)vehicles generally include one or more batteries. Each battery isgenerally composed of a plurality of electrochemical cells (i.e., cells)combined in series to produce a potential. The smallest unit (i.e.,grouping) of cells for which a state of charge (SOC) may be determinedis generally referred to as a module.

The cells and/or modules of the battery are generally matched bycapacities and voltages during the battery fabrication process. Thefabrication process may also include charging and discharging thebattery to confirm that all module voltages are within a specifiedtolerance at all voltage levels. The assembly process generally providesa battery having module voltages within a few milli-volts of oneanother.

Over time, ambient conditions and/or charging/discharging the batteryduring vehicle operation may result in differences among the individualSOC of the cells (SOC_(cell)). The SOC_(cell) variations are generallyobserved as divergence in module voltages (i.e., states of charge) sincea module is generally the smallest grouping (i.e., unit) of cells forwhich a state of charge (SOC) may be determined.

Conventionally, the batteries are controlled between predefined minimumand maximum SOC limits to prevent over-discharge and over-charge of anycell within the battery. When a module approaches the minimum SOC limit,the battery discharge current is driven to zero. When a moduleapproaches the maximum SOC limit, the battery charge current is drivento zero. Thus, any divergence among SOC modules may reduce the operatingrange of the battery which may, in turn, result in reduced batteryperformance and a reduced battery life. Accordingly, it is generallydesirable to rebalance the battery when a divergence among module SOC isidentified.

Conventional methods for rebalancing the battery (i.e., reducing oreliminating module SOC divergence) require low-rate constant-currentovercharge of the cells/modules. Such low-rate constant-currentovercharge generally requires precise control of charge current (e.g., 1to 2 Amperes) and may require a long period of time (e.g., 5 hours ormore) to complete.

Conventional hybrid and fuel cell vehicle charge-control systems aregenerally not configured to control the charge current within theconventional rebalancing range during vehicle operation. Furthermore,during recharging of the cells (i.e., battery recharging), the vehiclemay experience decreased operating performance (e.g., poor vehicleacceleration, reduced fuel economy, etc.). The decreased vehicleperformance may result in a vehicle operator perceiving different orunusual vehicle behavior.

Conventional recharging of a pure electric vehicle generally rebalancesthe cells of the EV battery. Such rebalancing of EV batteries isgenerally possible because the vehicle is plugged into a steady powersupply (e.g., the United States power grid) and allowed to slowly chargeto a full SOC during EV recharging. The slow charging process inherentlyrebalances the SOC of the cells. However, rapid EV recharge techniquesare under development which may reduce the inherent rebalancing of an EVbattery during EV recharging. Accordingly, purely electric vehicles mayalso require a system and method for rebalancing a battery duringvehicle operation.

Therefore, a system and method for rebalancing a battery (i.e., thecells of the battery, the modules of the battery, etc.) during vehicleoperation may be desirable. Furthermore, a system and method forrebalancing a battery during vehicle operation that reduces and/oreliminates recharge related vehicle performance degradation and/orimproves control of the charge current may be desirable.

SUMMARY OF THE INVENTION

Accordingly, one or more embodiments of the present invention mayprovide a system and/or method for rebalancing a battery during vehicleoperation that reduces and/or eliminates recharge related vehicleperformance degradation and/or improves control of the charge currentduring battery rebalancing.

In at least one embodiment of the present invention, a method forrebalancing a battery in a vehicle during vehicle operation, the batteryincluding a plurality of modules, is provided. The method may includedetermining when an automatic rebalance mode start condition issatisfied, modifying a target state of charge for the battery at leastin part in response to the start condition being satisfied such that thetarget state of charge is raised from a standard operating value to arebalance value, operating the vehicle with the target state of chargeat the rebalance value, determining when an automatic rebalance mode endcondition or an interrupt condition is satisfied, and modifying thetarget state of charge in response to the automatic rebalance mode endcondition or the interrupt condition being satisfied such that thetarget state of charge is lowered from the rebalance value to thestandard operating value.

In at least one other embodiment of the present invention, a system forrebalancing a battery in a vehicle during vehicle operation is provided.The system may include a battery having a plurality of modules whereineach of the modules includes one or more cells, and a controller inelectronic communication with the battery. The controller may determinewhen an automatic rebalance mode start condition is satisfied, modify atarget state of charge for the battery at least in part in response tothe start condition being satisfied such that the target state of chargeis raised from a standard operating value to a rebalance value,determine when an automatic rebalance mode end condition or an interruptcondition is satisfied, and modify the target state of charge inresponse to the end condition or the interrupt condition being satisfiedsuch that the target state of charge is lowered from the rebalance valueto the standard operating value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a system for rebalancing abattery in a vehicle during vehicle operation according to oneembodiment of the present invention;

FIG. 2 is a flow diagram of a method for rebalancing a battery in avehicle during vehicle operation according to one embodiment of thepresent invention; and

FIGS. 3 (a-c) are charge efficiency versus SOC curves corresponding tovarious steps of a method for rebalancing a battery in a vehicle duringvehicle operation according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, a block diagram illustrating a system 100 forrebalancing a battery in a vehicle (i.e., electric vehicle, hybridelectric vehicle, fuel cell vehicle, etc.) during vehicle operationaccording to one embodiment of the present invention is shown. Thesystem may include a controller 102, a battery 104, a cruise controlactuator 106, a vehicle speed sensor 108, and/or a diagnostic device110.

The controller 102 may be electronically coupled to the battery 104, thecruise control actuator 106, the vehicle speed sensor 108 and/or thediagnostic device 110 such that electronic signals may be transmittedbetween the controller 102 and one or more components (i.e., 104, 106,108, 110) of the system 100. In general, the controller 102 may includea processor and/or other electronic device (e.g., an ApplicationSpecific Integrated Circuit and/or the like) which executes softwareapplication programs, executes firmware, and/or which performs otherlogical exercises. In at least one embodiment of the present invention,the controller 102 may execute the method 200 described in detail inconnection with FIG. 2.

It is contemplated that all or part of the functionality of thecontroller 102 may be incorporated into a single controller as shown inFIG. 1, such as a vehicle system controller (VSC). Alternatively, thefunctionality of the controller 102 may be distributed among a pluralityof controllers (not shown). Controller inputs and outputs (i.e.,electronic signals) may be received and passed between controllers via aController Area Network (CAN), dedicated communication wires, and thelike.

The battery 104 generally includes one or more modules 112. Similarly,each module 112 may include one or more cells (e.g., electrochemicalcells) 114 for storing energy and producing a potential. A module 112 isgenerally the smallest unit (i.e., grouping) of cells 114 for which astate of charge (SOC) may be determined by the system 100.

In the exemplary embodiment shown in FIG. 1, the battery 104 includesfour modules 112 and each module 112 further includes five cells 114. Inat least one other embodiment of the present invention, each module 112may include a single (i.e., only one) cell 114 such that the number ofmodules 112 is equal to the number of cells 114. However, the battery104 may include any appropriate quantity of modules 112 and each module112 may further include any appropriate quantity of cells 114 to meetthe design criteria of a particular application. Furthermore, in atleast one embodiment of the present invention, each module 112 includesthe same number of cells 114 (e.g., each module 112 of FIG. 1 includesfive cells 114). However, it is contemplated by the present inventionthat a first module 112 may include more or less cells 114 than a secondmodule 112 to meet the design criteria of a particular application.

In at least one embodiment of the present invention, the cruise controlactuator 106 is a switch and/or other device (not shown) electronicallycoupled to the controller 102 for transmitting a vehicle constant speedcontrol request from an operator (not shown).

In at least one other embodiment of the present invention, the cruisecontrol actuator 106 may include a speed control controller (not shown),a switch, and/or other device for controlling the vehicle to a constanttarget speed (i.e., cruise control setpoint, speed control setpoint,etc.). In such an embodiment, the cruise control actuator 106 may beelectronically coupled to the controller 102 for providing an indication(e.g., electronic signal) that the vehicle is operating in a constantspeed control mode (i.e., cruise control mode) and/or for providing asignal corresponding to the speed control setpoint. However, the cruisecontrol actuator 106 may be any appropriate device or group of devicesfor engaging a vehicle constant speed control mode (i.e., for placingthe vehicle in a cruise control mode).

The vehicle speed sensor 108 may be any device capable of determiningdirectly and/or indirectly the speed of a vehicle to which the battery104 is electronically coupled. The vehicle speed sensor 108 is generallyelectronically coupled to the controller 102 and/or the cruise controlactuator 106 for providing a signal corresponding to the vehicle speed.

The diagnostic device 110 may be any device capable of electronicallycoupling to one or more components (e.g., 102, 104, 106, 108) of thesystem 100 for performing diagnostic (i.e., troubleshooting, evaluation,etc.) functions, such as a hand held computer, a hardware based device,and the like.

Referring to FIG. 2, a flow diagram of a method 200 for rebalancing abattery in a vehicle during vehicle operation according to oneembodiment of the present invention is shown. The method 200 may beadvantageously implemented in connection with the system 100, describedpreviously in connection with FIG. 1, and/or any appropriate system tomeet the design criteria of a particular application. The method 200generally includes a plurality of blocks or steps (e.g., 202, 204, 206,208, 210, 212, 214) that may be performed serially. As will beappreciated by one of ordinary skill in the art, the steps of the method200 may be performed in at least one non-serial (or non-sequential)order, and one or more steps may be omitted to meet the design criteriaof a particular application.

Decision block 202 generally determines (i.e., detects, identifies,etc.) when a pre-condition is satisfied. When satisfaction of thepre-condition is detected (i.e., the YES leg of decision block 202), themethod may proceed to decision block 204. Otherwise, the methodgenerally remains at decision block 202 (i.e., the NO leg of decisionblock 202).

In one exemplary embodiment of the present invention, the pre-conditionmay be satisfied when the vehicle is operating in a cruise control mode(i.e., constant speed control mode). In general, vehicle power demand isrelatively constant for a vehicle operating in a constant speed controlmode, as compared with a vehicle not operating at a constant speed.Accordingly, satisfying the pre-condition when the vehicle is in acruise control mode may provide improved control over the rebalancingcharge current. Improved control over the rebalancing charge current mayalso provide a decrease in battery heating during the rebalancingprocess. In at least one embodiment of the present invention, a cruisecontrol actuator (e.g., 106) may place the vehicle in the cruise controlmode in response to a vehicle operator (i.e., operator) initiatedcommand.

In another exemplary embodiment of the present invention, thepre-condition may be satisfied when the vehicle is operating in a cruisecontrol mode for a predetermined duration of time (e.g., thepre-condition may be satisfied when the vehicle has been operating in acruise control mode for one or more minutes). By delaying satisfactionof the pre-condition until the vehicle has operated in cruise controlmode for a predetermined duration, the probability that the method 200will operate to completion once started may be increased. Such increasedprobability may result from an increased probability that the operatorintends the vehicle to remain in cruise control mode once the operatorhas allowed the vehicle to operate in cruise control mode for thepredetermined duration of time.

In yet another exemplary embodiment of the present invention, decisionblock 202 further includes the step of determining a speed of thevehicle (i.e., vehicle speed). The vehicle speed may be determined usingany appropriate device and/or algorithm to meet the design criteria of aparticular application, such as a vehicle speed sensor (e.g., 108), asignal from a cruise control actuator (e.g., 106) corresponding to aspeed control setpoint, and the like. Furthermore, the pre-condition maybe satisfied when the vehicle is operating in a cruise control mode andthe speed is greater than or equal to a predetermined minimum cruisespeed (SPEED_(min)) and less than or equal to a predetermined maximumcruise speed (SPEED_(max)). In at least one embodiment of the presentinvention, SPEED_(min) may equal 40 miles per hour and SPEED_(max) mayequal 85 miles per hour. In at least one other embodiment of the presentinvention, SPEED_(min) may equal 45 miles per hour and SPEED_(max) mayequal 75 miles per hour. However SPEED_(min) and SPEED_(max) may equalany appropriate values to meet the design criteria of a particularapplication. It may be observed that the probability of the vehicleremaining in a cruise control mode may be a function of the speed atwhich the vehicle is operating. For example, an operator who has set thecruise control mode to control the speed of the vehicle to 35 miles perhour is likely to be operating the vehicle on city streets (i.e.,requiring frequent stops). In contrast, an operator who has set thecruise control mode to control the speed of the vehicle to 65 miles perhour is likely to be operating the vehicle on a highway (i.e., requiringfew stops). Accordingly, by delaying satisfaction of the pre-conditionuntil the vehicle is operated at a speed within the range of SPEED_(min)and SPEED_(max), the probability that the method 200 will operate tocompletion once started may be increased.

In still yet another embodiment of the present invention, thepre-condition is satisfied when the vehicle is operating in a cruisecontrol mode for a predetermined duration, the speed is greater than orequal to a predetermined minimum cruise speed, and the speed is lessthan or equal to a predetermined maximum cruise speed.

The above exemplary embodiments are illustrative and non-limiting.Accordingly, the pre-condition may be satisfied in response to anyappropriate stimulus (e.g., action, occurrence, signal, trigger, and thelike) to meet the design criteria of a particular application.Furthermore, decision block 202 may be omitted to meet the designcriteria of a particular application.

Decision block 204 generally determines when an automatic rebalance modestart condition (i.e., start condition) is satisfied. When satisfactionof a start condition is detected (i.e., the YES leg of decision block204), the method may proceed to step 206. Otherwise, the methodgenerally returns to decision block 202 (i.e., the NO leg of decisionblock 204).

In one exemplary embodiment of the present invention, decision block 204further includes the steps of determining a throughput for the battery(i.e., battery throughput, the absolute value of charge and dischargecurrent integrated over a period of time) since the last successfulrebalance of the battery (i.e., since it is determined that an automaticrebalance mode end condition is satisfied), determining a SOC for eachmodule (i.e., module SOCs) when the vehicle is operating with a targetstate of charge for the battery (i.e., a desired average of the moduleSOCs, a target average of the module SOCs) at (i.e., set equal to) astandard operating value (e.g., 50%), and determining a maximum SOC(SOC_(mod,max)) and minimum SOC (SOC_(mod,min)) from the module SOCs. Aspreviously stated in connection with FIG. 1, a module is generally thesmallest grouping of cells for which a SOC may be determined.Accordingly, each module SOC represents one or more cell SOCs. Acontroller (e.g., 102) and/or other electronic device may beelectronically coupled to the battery (e.g., 104) for performing one ormore of the steps of the method 200. The start condition may besatisfied when a difference between SOC_(mod,max) and SOC_(mod,min) isgreater than or equal to a predetermined upper delta limit (Δ_(UL))and/or the battery throughput is greater than or equal to apredetermined minimum throughput value (TPV_(min)). In at least oneembodiment of the present invention, Δ_(UL) may be substantially equalto 10% and/or TPV_(min) may be substantially equal to (i.e.,approximately) 1800 Amp Hours.

In another exemplary embodiment of the present invention, decision block204 further includes the step of determining the battery throughputsince the last successful rebalance of the battery (i.e., sincesatisfaction of the automatic rebalance mode end condition), and thestart condition is generally satisfied when the battery throughput isgreater than or equal to a predetermined minimum throughput threshold(TPT_(min)), such as 3600 Amp Hours.

In yet another exemplary embodiment of the present invention, decisionblock 204 further includes the step of determining a discharge power forthe battery (i.e., battery discharge power) and the start condition maybe satisfied when the battery discharge power is less than or equal to apredetermined lower discharge limit (DC_(LL)).

In still yet another exemplary embodiment of the present invention, thestart condition may be satisfied by a command (i.e., signal, electronicsignal) from a diagnostic device (e.g., 110), such as a diagnosticdevice used by a service technician.

The above exemplary embodiments are illustrative and non-limiting.Accordingly, the start condition may be satisfied in response to anyappropriate stimulus (e.g., action, occurrence, signal, trigger, and thelike) to meet the design criteria of a particular application.

At step 206, the target SOC (i.e., the desired average of the moduleSOCs), is modified such that the target SOC is raised (i.e., moved,increased, etc.) from a standard operating value (e.g., 50%) to arebalance value (e.g., 80%). In at least one embodiment of the presentinvention, the modification is performed gradually such as by using aramp function, a logarithmic function, and the like (i.e., a non-stepfunction). As will be discussed in connection with FIG. 3 b, therebalance value may correspond generally to a point on the SOC v. ChargeEfficiency Curve where the charge efficience begins to decline rapidly.

At step 208, the vehicle is operated with the target SOC at therebalance value. When the vehicle is operating at the rebalance value,the discharge efficiency of each battery module is generally equal.However, the charge efficiency is generally lower for modules having aSOC near SOC_(mod,max). Accordingly, when the system (e.g., 100) ischarging the battery (e.g. 104), modules (e.g., 112) near SOC_(mod,min)are generally charged more than modules near SOC_(mod,max). Such unequalcharging generally decreases the difference between SOC_(mod,max) andSOC_(mod,min).

In at least one embodiment of the present invention, the period of timerequired to rebalance the battery (e.g., duration of step 208) may bereduced by initiating (i.e., performing) a plurality of battery pulses(i.e., pulsing the battery). Each battery pulse generally includes thesteps of charging (e.g., rapidly charging) the battery to apredetermined charge pulse value and subsequently discharging thebattery to a predetermined discharge pulse value or zero pulse value.Pulsing the battery may be particularly beneficial when vehicle demandon the battery is low since low vehicle demand may result in infrequentcharging and discharging of the battery.

Furthermore, pulsing the battery may reduce thermodynamic inefficienciesof the rebalance process, thereby enabling more complete rebalance withless total heat generation and concomitant energy losses. Suchembodiments may provide pulse charging at higher currents where chargeefficiencies are greater for some electrochemical systems (e.g., anickel-metal hydride battery system). Such embodiments may also provideelectrochemical discharging of a portion of charge side-reactionproducts which would otherwise have to chemically recombine to form heat(e.g., oxygen with hydrogen in a nickel-metal hydride battery system).

Decision block 210 generally determines (i.e., detects, identifies,etc.) when an automatic rebalance mode interrupt condition (i.e.,interrupt condition) is satisfied. When satisfaction of an interruptcondition is detected (i.e., the YES leg of decision block 210), themethod may proceed to step 214. Otherwise, the method generally fallsthrough to decision block 212 (i.e., the NO leg of decision block 210).

In one exemplary embodiment of the present invention, decision block 210further includes the step of determining a cell temperature for one ormore cells of the battery. A controller and/or other electronic devicemay be electronically coupled to the battery for determining celltemperatures. The interrupt condition may be satisfied when the celltemperature for one or more cells is determined to be greater than apredetermined maximum cell temperature and/or less than a predeterminedminimum cell temperature. The temperature of one or more cells may bemeasured indirectly by measuring the temperature of a module includingthe one or more cells. Accordingly, the interrupt condition may besatisfied when the temperature for one or more modules is determined tobe greater than a predetermined maximum cell temperature and/or lessthan a predetermined minimum cell temperature.

In another exemplary embodiment of the present invention, decision block210 further includes the step of determining cell temperatures for aplurality of cells of the battery (i.e., determining a plurality of celltemperatures). A controller and/or other electronic device may beelectronically coupled to the battery for determining each celltemperature. The interrupt condition may be satisfied when a differencebetween a first cell temperature and a second cell temperature isgreater than or equal to a predetermined temperature delta value. Thetemperature of one or more cells may be measured indirectly by measuringthe temperature of a module including the one or more cells.Accordingly, the interrupt condition may be satisfied when a differencebetween a first module temperature and a second module temperature isgreater than or equal to the predetermined temperature delta value.

In yet another exemplary embodiment of the present invention, theinterrupt condition may be satisfied when the step of operating thevehicle with the target state of charge at the rebalance value (i.e.,step 208) is performed for a predetermined maximum time (i.e., themethod 200 times out).

The above exemplary embodiments are illustrative and non-limiting.Accordingly, the interrupt condition may be satisfied in response to anyappropriate stimulus (e.g., action, occurrence, signal, trigger, and thelike) to meet the design criteria of a particular application.

Decision block 212 generally determines (i.e., detects, identifies,etc.) when an automatic rebalance mode end condition (i.e., endcondition) is satisfied. When satisfaction of an end condition isdetected (i.e., the YES leg of decision block 212), the method mayproceed to step 214. Otherwise, the method generally returns to step 208(i.e., the NO leg of decision block 212).

In one exemplary embodiment of the present invention, decision block 212further includes the step of determining battery throughput when thevehicle is operating with the target state of charge at the rebalancevalue (i.e., when the vehicle is operating in step 208). The endcondition may be satisfied when the battery throughput is greater thanor equal to a predetermined maximum throughput value (TPV_(max)).

In another exemplary embodiment of the present invention, decision block212 further includes the steps of determining a SOC for each module(i.e., module SOCs) when the vehicle is operating with a target state ofcharge at a rebalance value, and determining a maximum SOC(SOC_(mod,max)) and minimum SOC (SOC_(mod,min)) from the module SOCs. Aspreviously stated in connection with FIG. 1, a module is generally thesmallest grouping of cells for which a SOC may be determined.Accordingly, each module SOC represents one or more cell SOCs. Acontroller (e.g., 102) and/or other electronic device may beelectronically coupled to the battery (e.g., 104) for performing one ormore of the steps of the method 200. The end condition may be satisfiedwhen a difference between SOC_(mod,max) and SOC_(mod,min) is less thanor equal to a predetermined lower delta limit (Δ_(LL)).

The above exemplary embodiments are illustrative and non-limiting.Accordingly, the end condition may be satisfied in response to anyappropriate stimulus (e.g., action, occurrence, signal, trigger, and thelike) to meet the design criteria of a particular application.

At step 214, the target SOC, is modified such that the target SOC islowered (i.e., moved, decreased, etc.) from the rebalance value (e.g.,80%) to the standard operating value (e.g., 50%). In at least oneembodiment of the present invention, the modification is performedgradually such as by using a ramp function, a logarithmic function, andthe like (i.e., a non-step function). In at least one other embodimentof the present invention, the modification is performed gradually inresponse to satisfaction of an end condition and the modification isperformed rapidly in response to satisfaction of an interrupt condition.However, the modification may be performed using any appropriatefunction (e.g., step function, non-step function, ramp function, etc.)in response to any appropriate trigger (e.g., satisfaction of an endcondition, satisfaction of an interrupt condition) to meet the designcriteria of a particular application.

It is contemplated by the present invention that the target state ofcharge may be a discrete value, such as 50%, or a range of values, suchas 48%-52%. Accordingly, the standard operating value and/or therebalance value may be a discrete value or a range of values.

Referring to FIGS. 3 (a-c), charge efficiency versus SOC curvescorresponding to various steps of a method (e.g., the method 200) forrebalancing a battery in a vehicle during vehicle operation according toone embodiment of the present invention are provided. As illustrated inFIGS. 3 (a-c), one or more limits may be established about the targetstate of charge (i.e., target SOC). The one or more limits may beimplemented in connection with any appropriate system (e.g., the system100) and/or method (e.g., the method 200) to meet the design criteria ofa particular application. A minimum SOC limit (SOC_(min)) may representa minimum threshold below which the system and/or method will notdischarge the battery when a module SOC is below the minimum threshold.Similarly, a maximum SOC limit (SOC_(max)) may represent a maximumthreshold above which the system and/or method will not charge thebattery when a module SOC is above the maximum threshold. The minimumthreshold and maximum threshold may protect the battery from damagecaused by operating the battery in an undercharge and/or overchargestate.

generally represents a vehicle operating at a target SOC equal to astandard operating value (i.e., SOV) of 50% (e.g., a vehicle operatingin step 204 of method 200). In the exemplary embodiment shown in FIG. 3a, the minimum threshold (i.e., SOC_(min), minimum standard SOC limit)is set to 30% and the maximum threshold (i.e., SOC_(max), maximumstandard SOC limit) is set to 70%. Accordingly, the vehicle, via one ormore controllers such as a vehicle control system, will not dischargethe battery when any module SOC (i.e., average SOC of the cells of amodule) is below 30%. Similarly, the vehicle will not charge the batterywhen any module SOC is above 70%.

FIG. 3 b generally represents a vehicle operating at a target SOC equalto a rebalance value (i.e., RBV) of 80% (e.g., a vehicle operating instep 208 of method 200). In the exemplary embodiment shown in FIG. 3 b,the minimum threshold (i.e., SOC_(min), minimum rebalance SOC limit) hasbeen increased to 60% and the maximum threshold (i.e., SOC_(max),maximum standard SOC limit) has been increased to 90%. Accordingly, thevehicle, via one or more controllers such as a vehicle control system,will not discharge the battery when any module SOC is below 60%.Similarly, the vehicle will not charge the battery when any module SOCis above 90%.

In at least one embodiment of the present invention, the minimumthreshold may be increased by the difference between the rebalance valueand the standard operating value such that the amount of discharge poweravailable to the vehicle during rebalance is substantially maintained.In at least one other embodiment of the present invention, the minimumthreshold may be held constant (i.e., not modified, not raised, notlowered etc.), such as at 30%. In contrast, the maximum threshold isgenerally increased such that the maximum threshold is only slightlygreater than (i.e., greater than but substantially near) the rebalancevalue. By increasing the maximum threshold during rebalance asdescribed, the probability of damaging the battery via overcharging maybe reduced. However, the minimum and maximum thresholds may be set toany appropriate values to meet the design criteria of a particularapplication.

FIG. 3 c generally represents a vehicle operating at a target SOC equalto a standard operating value of 50% after successful completion of arebalance sequence (e.g., a vehicle operating in step 214 of method200). The FIG. 3 c is substantially similar to the FIG. 2 a with theexception that the module SOCs have been rebalanced such that thedifference between SOC_(mod,max) and SOC_(mod,min) is reduced.

In accordance with various embodiments of the present invention, themethods described herein are intended for operation as software and/orfirmware running on a processor and/or other electronic device.Dedicated hardware implementations including, but not limited to,Application Specific Integrated Circuits, programmable logic arrays andother hardware devices can likewise be constructed to implement themethods described herein.

It should also be noted that the software implementations of the presentinvention as described herein are optionally stored on a tangiblestorage medium, such as: a magnetic medium such as a disk or tape; amagneto-optical or optical medium such as a disk; or a solid statemedium such as a memory card or other package that houses one or moreread-only (non-volatile) memories, random access memories, or otherre-writable (volatile) memories. A digital file attachment to email orother self-contained information archive or set of archives isconsidered a distribution medium equivalent to a tangible storagemedium. Accordingly, the invention is considered to include a tangiblestorage medium or distribution medium, as listed herein and includingart-recognized equivalents and successor media, in which the softwareimplementations herein are stored.

Accordingly, one or more embodiments of the present invention mayprovide a system and/or method for rebalancing a battery during vehicleoperation that reduces and/or eliminates recharge related vehicleperformance degradation and/or improves control of the charge currentduring battery rebalancing. In particular, one or more embodiments ofthe present invention may provide a system and method for rebalancing abattery during vehicle operation while substantially maintaining vehiclefuel efficiency and/or vehicle responsiveness.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

1. A method for rebalancing a battery in a vehicle during vehicleoperation, the battery including a plurality of modules, the methodcomprising: determining when an automatic rebalance mode start conditionis satisfied; modifying a target state of charge for the battery atleast in part in response to the start condition being satisfied, suchthat the target state of charge is raised from a standard operatingvalue to a rebalance value; operating the vehicle with the target stateof charge at the rebalance value; determining when an automaticrebalance mode end condition or an interrupt condition is satisfied; andmodifying the target state of charge in response to the automaticrebalance mode end condition or the interrupt condition being satisfied,such that the target state of charge is lowered from the rebalance valueto the standard operating value.
 2. The method of claim 1 furthercomprising: determining a throughput for the battery after it isdetermined that the automatic rebalance mode end condition is satisfied;determining a state of charge for each of the modules when the vehicleis operating with the target state of charge at the standard operatingvalue; determining a maximum state of charge from the determined stateof charge for each of the modules; and determining a minimum state ofcharge from the determined state of charge for each of the modules, andwherein the automatic rebalance mode start condition is satisfied whenat least one of a difference between the maximum state of charge and theminimum state of charge is greater than or equal to a predeterminedupper delta limit and the throughput is greater than or equal to apredetermined minimum throughput value.
 3. The method of claim 2 whereinthe predetermined upper delta limit is substantially 10% and thepredetermined minimum throughput value is substantially 1800 Amp Hours.4. The method of claim 1 further comprising: determining a dischargepower for the battery, and wherein the automatic rebalance mode startcondition is satisfied when the battery discharge power is less than orequal to a predetermined lower discharge limit.
 5. The method of claim 1wherein the automatic rebalance mode start condition is satisfied by acommand from a diagnostic device.
 6. The method of claim 1 furthercomprising determining when a pre-condition is satisfied, wherein thepre-condition is satisfied when the vehicle is operating in a cruisecontrol mode, and the step of modifying a target state of charge for thebattery such that the target state of charge is raised from a standardoperating value to a rebalance value is performed in response to boththe pre-condition and the start condition being satisfied.
 7. The methodof claim 6 wherein the pre-condition is satisfied when the vehicle isoperating in a cruise control mode for a predetermined duration.
 8. Themethod of claim 6 further comprising: determining a speed of thevehicle, and wherein the pre-condition is satisfied when the vehicle isoperating in a cruise control mode, the speed is greater than or equalto a predetermined minimum cruise speed, and the speed is less than orequal to a predetermined maximum cruise speed.
 9. The method of claim 6further comprising: determining a speed of the vehicle, and wherein thepre-condition is satisfied when the vehicle is operating in a cruisecontrol mode for a predetermined duration, the speed is greater than orequal to a predetermined minimum cruise speed, and the speed is lessthan or equal to a predetermined maximum cruise speed.
 10. The method ofclaim 1, each of the modules comprising one or more cells, the methodfurther comprising: determining a cell temperature for one or more ofthe cells of the battery, and wherein the interrupt condition issatisfied when the cell temperature for one or more cells of the batteryis greater than a predetermined maximum cell temperature or less than apredetermined minimum cell temperature.
 11. The method of claim 1, eachof the modules comprising one or more cells, the method furthercomprising: determining a cell temperature for each of two or more ofthe cells of the battery, and wherein the interrupt condition issatisfied when a difference between a first cell temperature and asecond cell temperature is greater than or equal to a predeterminedtemperature delta value.
 12. The method of claim 1 wherein the interruptcondition is satisfied when the step of operating the vehicle with thetarget state of charge at the rebalance value is performed for apredetermined maximum time.
 13. The method of claim 1 furthercomprising: determining a throughput for the battery when the vehicle isoperating with the target state of charge at the rebalance value, andwherein the end condition is satisfied when the throughput is greaterthan or equal to a predetermined maximum throughput value.
 14. Themethod of claim 1 further comprising: determining a state of charge foreach of the modules when the vehicle is operating with the target stateof charge at the rebalance value; determining a maximum state of chargefrom the determined state of charge for each of the modules; anddetermining a minimum state of charge from the determined state ofcharge for each of the modules, and wherein the end condition issatisfied when a difference between the maximum state of charge and theminimum state of charge is less than or equal to a predetermined lowerdelta limit.
 15. The method of claim 1 further comprising: initiating aplurality of battery pulses when the vehicle is operating with thetarget state of charge at the rebalance value, wherein each batterypulse comprises the steps of charging the battery to a predeterminedcharge pulse value and subsequently discharging the battery to at leastone of a predetermined discharge pulse value and a zero pulse value. 16.The method of claim 1 wherein the rebalance value is substantially 80%.17. The method of claim 1 wherein the target state of charge is raisedfrom the standard operating value to the rebalance value using anon-step function.
 18. The method of claim 1 wherein the target state ofcharge is lowered from the rebalance value to the standard operatingvalue using a non-step function in response to the end condition beingsatisfied.
 19. The method of claim 1 further comprising: generatingmaximum and minimum standard state of charge limits corresponding to thestandard operating value; and generating maximum and minimum rebalancestate of charge limits corresponding to the rebalance value, and whereina difference between the rebalance value and the standard operatingvalue is substantially equal to a difference between the minimumrebalance state of charge limit and the minimum standard state of chargelimit, and a difference between the maximum standard state of chargelimit and the standard operating value is greater than a differencebetween the maximum rebalance state of charge limit and the rebalancevalue.
 20. A system for rebalancing a battery in a vehicle duringvehicle operation, the system comprising: a battery having a pluralityof modules, wherein each of the modules includes one or more cells; anda controller in electronic communication with the battery fordetermining when an automatic rebalance mode start condition issatisfied, modifying a target state of charge for the battery at leastin part in response to the start condition being satisfied such that thetarget state of charge is raised from a standard operating value to arebalance value, determining when an automatic rebalance mode endcondition or an interrupt condition is satisfied, and modifying thetarget state of charge in response to the end condition or the interruptcondition being satisfied such that the target state of charge islowered from the rebalance value to the standard operating value. 21.The system of claim 20 further comprising: a cruise control actuator forplacing the vehicle in a cruise control mode; and a vehicle speed sensorfor determining a speed of the vehicle, and wherein the controllerdetermines when a pre-condition is satisfied and modifies a target stateof charge for the battery in response to both the pre-condition and thestart condition being satisfied such that the target state of charge israised from a standard operating value to a rebalance value, thepre-condition being satisfied when the vehicle is operating in thecruise control mode for a predetermined duration, the speed is greaterthan or equal to a predetermined minimum cruise speed, and the speed isless than or equal to a predetermined maximum cruise speed.
 22. Thesystem of claim 20 wherein the controller initiates a plurality ofbattery pulses when the vehicle is operating with the target state ofcharge at the rebalance value, and each battery pulse comprises chargingthe battery to a predetermined charge pulse value and subsequentlydischarging the battery to at least one of a predetermined dischargepulse value and a zero pulse value.
 23. The method of claim 1 whereinthe automatic rebalance mode start condition is satisfied when thevehicle is operating in a cruise control mode.